1. Field of the Invention
The present invention relates to a photodiode arrangement which receives light, especially ultraviolet rays to generate a current.
2. Description of the Related Art
In a conventional photodiode, an N+ diffusion layer which has an N-type impurity diffused therein with a high concentration and is formed into a comb shape like “E” and a P+ diffusion layer which has a P-type impurity diffused therein with a high concentration and is formed into a shape like “π” are laterally arranged to face each other in a silicon semiconductor layer having an N-type impurity diffused therein with a low concentration on an SOI (Silicon On Insulator) substrate which has the silicon semiconductor layer with a thickness of approximately 150 nm formed on a silicon substrate to sandwich a buried oxide film there between in such a manner that a comb tooth portion of the N+ diffusion layer meshes with a comb tooth portion of the P+ diffusion layer, and a predetermined voltage is applied to a metal wiring line electrically connected with the N+ diffusion layer and the P+ diffusion layer to detect an intensity of an ultraviolet ray (see, e.g., Japanese Patent Application Laid-open No. 162024-1995, p. 4, paragraph 0025-p. 4, paragraph 0035, and FIGS. 2 and 3).
At the present time, the amount of ultraviolet irradiation is increasing due to destruction of the ozone layer and concern over the influence of ultraviolet rays contained in solar light on the human body and/or the environment is increasing.
In general, an ultraviolet ray is invisible light in an ultraviolet range of a wavelength of 400 nm or below. The ultraviolet ray is classified into a long-wave ultraviolet ray (an UV-A wave: a wavelength of approximately 320 to 400 nm), a medium-wave ultraviolet ray (an UV-B wave: a wavelength of approximately 280 to 320 nm), and a short-wave ultraviolet ray (an UV-C wave: a wavelength of approximately 280 nm or below). The influence on the human body and/or the environment varies depending on these wavelength ranges. It is considered that the UV-A wave darkens skin and reaches inner skin to cause aging, the UV-B wave inflames skins to possibly provoke skin cancer, and the UV-C wave has a strong bactericidal function but is absorbed in the ozone layer.
Therefore, demand for development of a sensor which separates ultraviolet rays in these three wavelength ranges and detects intensities of these ultraviolet rays has increased.
However, in the above-explained conventional technology, although a total amount of ultraviolet rays in the ultraviolet range of the wavelength of 400 nm or below can be detected, the three wavelength ranges have not as yet been separated for detection.